Wire treating furnace



Oct. 15, 1940. E. B. POWELL WIRE TREATING FURNACE Filed Fb. 2a, 1939 2Sheets-Shet 1 INVEN TOR. EVERTON B. POWELL 0% 5, 1940-. E. B. POWELLWIRE TREATING FURNACE Filed Feb. 28, 1939 2 Sheets-Sheet 2 m u m r E Mw. w 0 m Q M .A 4 r W q H II I H Patented Oct. 15, 1940 WIRE TREATINGFURNACE Everton B. Powell, Maplewood, N. J., assignor to RadioCorporation of America, a corporation of Delaware Application February28, 1939, Serial N 0. 258,880

3 Claims.

My invention relates to furnaces, particularly to furnaces for heating,in an atmosphere of desired gases, a plurality of continuously movingwires or strips of metal,

Wire is commonly heat treated either by placing large spools of the wirein a closed oven or by slowly reeling the wire through a heated tube,the speed of reeling being proportional for given time and temperatureto the length of the heated l0 tube.

be the speed of the wire through the furnace. Since wire of most metalsmust be heated in an atmosphere of reducing gas, such as hydrogen, toprevent excessive oxidation, and because a ll heating tube through whichthe wire is drawn must be open at its ends, a rather fast moving streamof gas through the tube must be'provided to completely envelope thewire; The gas escapes from the ends of the tube and, in furnaces ofconventional construction, where the tubes are short and the wire speedis low, the gas wastage per foot of treated wires is considerable. It isdifllcult, however, to make long furnaces. Either ceramic or refractorymetal tubes must be used,

with exterior heating means, but the few refractory metals available forfurnace tubes for continuous operation at high temperatures aredifflcult'to work and expensive, and long straight tubes of ceramicmaterial cannot be made because of brittleness, structural weakness, anda tendency to warp when heated.

An object of my invention is a furnace for continuously heating a movingwire in a gaseous atmosphere with means for reducing waste of gas.

'Another object of my invention is a furnace with heated ceramic tubesof any desired length for continuously heat treating: wire.

A more specific object jmy invention is a o furnace for heat treating aumber of wires, the furnaces being of any desired length with a straightceramic tube for each wire treated and' so constructed and arranged thatindividual tubes may be easilyreplaced.

u; A further object of my invention is a furnace for simultaneously heattreating a plurality of continuously moving wires.

According to my invention, a relatively large number of wires reeledfrom their individual so spools are each drawn through a small ceramicheated tube. Each of the-small ceramic tubes, 24 in number and dividedinto three end-to-end sections, is, in the specific furnace hereinafterdescribed, supported in a unitary ceramic casing 5 which is surroundedthroughout the length of The shorter the furnace the slower must thefurnace with an electric heating element. The sections of the tubes andcasing are loosely fitted end-to-end and are supported on rollers topermit free longitudinal expansion, one end of the ceramic assemblybeing fixed and the other end being spring pressed to yieldingly holdthe sections straight and together. The several tubes and theirsurrounding casing with the. heating element areembedded in a mass ofpowdery heat insulating material in a gas-tight metal housing. 1. Gasadmitted to the housing is diffused through the ceramic walls of thecasing and thence through the. tube walls where the gas pressure is lowand uniform throughout the length of the tubes. The metal housing is agas reservoir 1 about the casing and tubes from which a quiescentenvelope of gas is obtained about the wiresin thetubes'.

The characteristic. features of my. invention are defined in theappended claims and one specific embodiment is described in thefollowing specification and shown in the accompanying drawings in whichFigures 1 and 1a are side elevations, partly in section, of my improvedfurnace in combination with wire reeling means at each end, thestructure in the two figures being divided along line X X tofacilitate'illustration on one sheet, Figure 2 is a longitudinal sectionview of my improved furnace showing the internal arrangement of partsand Figure 3 is a view of the .I left hand end of the furnace shown inFigure 2.

In Figures 1 and 1a. are'shown a plurality of reels I from which aredrawn wires 2 through treating baths and into the right hand end of myimproved furnace 3. Each wire passes through E an individual heatingtube and through aligned cooling tubes in cooling chamber 4 on to reels5 at the left end of the furnace assembly. While my improved furnace isshown in Figures 1 and 1a in combination with wire plating mechanism, itmay be used for annealing purposes only, where the wire passes directlyfrom the. unloading reels into the inlet end of the furnace. For nickelplating iron wire, for example, the particular baths shown in Figure 1may for purposes of illustration comprise first a caustic cleaner intank 6, a 20% solution of nitric acid for etching the wire'in tank I anda nickel electrolytic plat-, ing bath in-tank 8. Between each emersiontank may be various water rinse sprays. preferably tensioned on'thereels to hold the wire centrally in the tubes and prevent drag in theheating zone.

The furnace proper shown indetail in Figure 2 comprises a large metaltank 9, gas-tight for g The wire is 0 low pressure gas, closed at eachend with cast iron headers. Extending inwardly from the inlet header [0is an integral flange Ii rectangular in cross section with a flangecollar l2 telescoped over the end of the first section of the ceramiccasing l3. Two additional sections of the casing are fitted end-to-endwith the first, and are supported on rollers l4, preferably one rollerbeing under each section, to relieve the butt joints of the casing fromstrains. The header l5 at the other end of the furnace is movable andhas an integral inwardly extending flange l6 and flange collar IT forengaging the left hand end of the ceramic casing. This header flangeslides in close fitted engagement with the inner surface of the hood orcast iron extension l8 bolted gastight to the outer end of the housing,and is spring pressed against the end of the casing by springs l9compressed between adjustable stud bolts in the end of the springhousing 2| and guide posts 22 on the outer face of the movable header.To maintain uniform pressure against the end of the ceramic casing onespring is preferred at each corner of the header.

Transverse ceramic spacers or partitions 23 held preferably at thejunctions of the casing sections support the wire heating tubes 24. Thetubes are in end-to-end sections, adjacent ends of the sections restingin the spacers, and are free to move independently of the spacers. Thetubes are held against longitudinal displacement by a removable plate 25fitted over the inlet header at one end and by countersunk shoulders inthe movable header at the other end. A cracked tube may be easilyreplaced by remov ing the plate and sliding the damaged tube out theinlet end without disturbing the other tubes. While the spring pressedceramic casing and tube assembly is long and the sections sumcientlyrigid to remain straight, the assembly is strong and will not warp whenheated. Distinguished from furnaces of the usual construction, there isno practical limit to the length of the ceramic wire heat treating tubesor to the number of parallel tubes that may be placed side-by-sidewithin one heating element.

A commercial reducing gas, such as hydrogen, may be employed to preventoxidation of the wires as they are heated. The gas in my improvedfurnace is admitted under low pressure at three spaced points in thebottom of the furnace through gas pipes 26. The gas fills the entirespace in the housing and filters through the pores of the ceramic casingto the interior of the casing where it then passes through the pores ofthe ceramic tubes into their interior. An unglazed ceramic is quitepervious to hydrogen. The open space in the casing about the tubespermits the gas pressure to become uniform throughout the length of thecasing and permits uniform and low pressure distribution of the gasthroughout the interior of the tubes. There is substantially no gas flowalong the interior of the tubes and although the gas pressure is nearlyatmospheric, each wire is effectively enveloped in gas throughout itsheated length. If gas leakage about the edges of the spacers isinsufficient to permit even gas pressure throughout the casing, holesmay be provided through the spacers.

There is no gas pressure gradient between the ends of the tubes and thegas leakage from either end of the tubes is slight so that theconsumption is small and efiiciency is high.

Heat from the heating element 21 surrounding the ceramic casing,preferably in the form of a continuous heating ribbon wound from one endof the casing to the other and connected to insulating lead-in bushing,is emciently transferred through the quiescent mass of gas to the wiresto be treated. Heat flows readily from the heating ribbon inwardlythrough the ceramic walls of the casing and the hydrogen atmospheretransfers the heat with only slight temperature drop to the severaltubes, whereas outward heat flow is reduced to a minimum by thepowderedinsulating material 28 which fills the casing. One furnace withceramic tubes 90 inches long for simultaneously annealing twentyfournickel plated iron wires has produced good results with the wirestravelling at the rate of thirty feet per minute with the heating tubesmaintained at a temperatureof 850 C. This furnace whose housing is onlyabout 15 inches by 25 inches in cross section had an outside housingtemperature comfortable to the hand although consuming about fortykilowatts of heating power.

The housing may be of sheet metal and the ceramic casing and tubes maybe of commercial aluminum oxide or alundum" made with wall thicknessessufllcient for good mechanical strength and the ceramics should beunglazed. The housing around the ceramic casing is filled with a powderyinsulating material to a level near the top of'the housing. Good resultshave been obtained with highly calcined magnesium oxide powder. Goodresults, with high thermal efficiency, low ceramic breakage and highspeed wire annealing, has been obtained with tubes about 90 inches long,.740 inch outside diameter, .100 inch wall thickness and a casing withthe same length, 12 inches by 2.75 inches and .375 inch wall thickness.

To cool the wires, before removal from the hydrogen atmosphere, to atemperature below oxidation temperature, I have found that a coolingchamber 4 may conveniently be mounted directly on the outlet end of thefurnace. In this chamber is a plurality of metal pipes 29 aligned withthe heating tubes and joined water-tight with the end plates of thechamber. Water admitted to the inlet pipe fills the chamber, cools thepipes and effectively chills the wires before their exit to the reels.Thecooling chamber 4 is preferably fastened gas-tight to the hood ll sothat gas which leaks into the hood from the ends of tubes and around theedges of the header I5 can escape only by passing through theconstriction of the small relatively long cooling pipes.

A furnace for continuously heating moving wires in a gas atmosphereconstructedaccording to my invention is easy to erect, inexpensive tomaintain and is eflicient in operation. A furnace constructed accordingto my invention may be of any desired length and provision may be madefor simultaneously heat treatinggany desired number of continuouslymoving wires.

I claim:

1. A plurality of gas pervious refractory tubes arranged side-by-side, acooling pipe coaxial with each of said tubes, a gas pervious refractorycasing surrounding said tubes and a heating element surrounding saidcasing, a gas reservoir comprising a gas tight housing surrounding saidcasing for supplying a quiescent gaseous atmosphere'to the interior ofsaid tubes, said housing having a fixed header on one end with openingsfitted around one end of each of said tubes, one

end of said casing abutting said fixed header, a

movable header inside said housingat the other end of the housing andbeing spring pressed against the other end of said casing, the other endof said tubes abutting said movable header and being Iree to movelongitudinally, said other end of said housing being joined gas-tight tothe ends of saidcooling pipes, and a cooling compartment surroundingsaid pipes.

2. In combination in a wire treating apparatus, an elongated metalhousing, a fixed metal header closing and joined gas tight to one end ofsaid housing, a metal hood closing and joined gas tight to the other endof said housing, a siidable header in said hood with spring biasingmeans to press s'aid movable header toward said fixed header, a tubularcasing of gas pervious refractory material extending the length of saidmetal housing with its ends abutting the opposed faces of the fixed andmovable headers, a heating element surrounding said casing, and meansfor admitting gas to said casing, a plurality of open ended ceramictubes extending side-by-side through said casing with their endssupported in openings in said headers, a plurality of cooling pipesjoined gas tight at their rims in openings in said hood, said pipesbeing in axial alignment with said tubes.

3. A refractory wire heating assembly comprising a gas-tight housing, astraight elongated ceramic casing in said housing, said casingcomprising a plurality of butted end-to-end sections, a heating elementsurrounding said casing, a. plurality of side-by-side tubes extendinglongitudinally through said casing, each tube comprising a plurality ofend-to-end sections, a transverse partition in said casing supportingadjacent ends of the tube sections, the casing and tubes being fixed atone. end to one end of said housing, a slidable header, the other end ofsaid casing and said tubes abutting said slidable header, means to presssaid header against the ends of the tube and casing sections to hold thecasing and tubes straight and structurally rigid yet free to expandlengthwise, and a gas inlet to said housing.

EVERTON B. POWELL.

